The need for certain vehicles such as heavy duty dump trucks, semi-trailers and the like, to have at least one (and often more than one) designated wheel bearing axle suspension system(s) capable of being raised and lowered selectively into and out of load bearing engagement with the road surface, is well-known in the art. This need usually arises in order that the vehicle be capable of legally satisfying maximum highway weight limit laws, as well as to provide an additional measure of safety when the vehicle is loaded. In this respect, such maximum weight limit laws often mandate, not just a maximum vehicle weight, but further prescribe (e.g., as by the so-called “bridge formula”) that the required number of axles needed be spaced in such a manner so as to distribute the weight of the vehicle and its cargo over a selected length of the vehicle. Such extra axles and their attached suspension systems are often referred to as “auxiliary” axle suspension systems.
The ability to lawfully carry the maximum weight of the load (cargo) allowed by law often translates economically into maximized profit and a more economically efficient use of the vehicle. However, it is also known that when the vehicle has one or more auxiliary axles added to its standard front and rear axles, three basic drawbacks arise when the wheels of the auxiliary axle(s) are in road engagement. The first is that cornering can become difficult. The second is that fuel efficiency can be reduced. The third is that tire wear can increase.
To overcome these drawbacks, the truck/trailer suspension art over the years has designed and developed numerous auxiliary axle suspension systems which are provided with a mechanism which when activated, usually from the cab of the truck or trailer, enables the wheels to be selectively raised out of or lowered into load bearing engagement with the road surface, thus, mitigating (reducing) the above-described problems associated with auxiliary axle usage. Moreover, in those systems which are properly designed, when lowered into road engagement the suspension assumes its proper, safe and lawful share of the load. When not needed (e.g., when the truck is empty) properly designed suspensions can be activated to raise the wheels off the road surface a sufficient distance and maintain them at this distance from the road thereby preventing inadvertent road contact, even when experiencing a curb or road bed irregularity. In this way, the system provides prolonged tire life and less fuel usage while making cornering easier, because these “auxiliary” wheels can be lifted when cornering, or when otherwise not needed.
While numerous types of auxiliary lift axle suspension systems have been devised, only a relatively few have been recognized as safe and effective for their intended purpose, and/or found over the years to be truly commercially acceptable. In this respect, the truly effective, safe and commercially acceptable designs are generally recognized as falling into three basic lift axle suspension system configurations. They are: (1) the use of an inverted leaf spring as both the lift mechanism and as a longitudinal tracking beam, accompanied by an air bellows, deflated at lift position but when inflated against the leaf spring's upward bias, lowers the suspension into road engagement thereby achieving a full load bearing, air-ride characteristic (e.g., as disclosed in U.S. Pat. No. 3,285,621); (2) the use of a longitudinal, heavy, tracking beam and an opposing air-bellows arrangement at either end of the beam (as first pioneered in commercially successful form by Neway Corporation and later adopted by others); and (3) the use of various types of lift mechanisms in combination with a highly stable, weight reducing, parallelogram suspension configuration. Perhaps one of the most successful of this type of lift suspension is those embodiments disclosed in U.S. Pat. No. 5,403,031 and commercially known as the Paralift™ and Paralift Ultra™ systems of Hendrickson Corporation).
Each of these three basic designs has its own distinctive features, making it the choice of design among certain vehicle operators. Currently, however, most knowledgeable heavy duty truck and trailer operators recognize that for many commercial operations the characteristics resulting from the “parallelogram” type lift suspension give rise to the best performance, as compared to the other two types described above. For example, the parallelogram design is lighter in weight than the heavy duty beam type suspension, yet its parallel or at least substantially parallel (from a side view perspective) control arms located in approximately the same vertical plane, achieve a high degree of wheel “tracking” necessary for safety and acceptable tire life. Moreover, while parallelogram suspensions are generally heavier in weight than the automatic leaf spring lift-suspensions, the parallelogram design allows, in most instances, for much heavier loads to be safely carried, while achieving at least equal “tracking” as the leaf spring lift design. Still further, the parallelogram design usually allows the suspension to have a shorter overall design length than either of the two other designs, enabling it to be placed on certain vehicles where the leaf spring lift and/or beam type lift suspension will not fit.
While the parallelogram type suspension is currently a rather popular design of choice due to its advantageous features as set forth above, when adopted to become a “lift” suspension, difficulties have historically been experienced in devising an acceptable lift mechanism that is able to efficiently and reliably, over an acceptable useful life, perform its intended task (lifting and lowering the wheels effectively, safely and lawfully). Thus, a need arose in the art for a lift axle suspension system of the parallelogram type, for both steerable and non-steerable suspensions, which had a truly effective lift mechanism that can achieve the basic characteristics of: lawful operation, effective lift, efficient lowering, safe and effective suspension operation when in road engagement, and long life of the various parts, including the lift mechanism.
This need was largely met, with high commercial success, by the aforesaid unique, parallelogram-type lift axle suspension systems as disclosed in the aforesaid U.S. Pat. No. 5,403,031 (with or without its unique axle caster adjusting feature). Moreover, in certain of the embodiments disclosed in this '031 patent, another problem attendant various former lift suspensions known as the “accordion effect,” (which tended to shorten the life of the lift bellows), was overcome without the, heretofore thought necessary, use of heavy, weight-adding, pivot bracketry.
The '031 patent's design achieved its improved results in this respect through the use of a structure which enabled the lift bellows to expand and contract bi-directionally in a highly efficient manner, while achieving at the same time, as a true parallelogram-type suspension, the known advantage of this type of suspension. In addition, weight was reduced over the known heavy beam type suspensions and life expectancy of the lift bellows was increased due to the elimination of the “accordion effect” (a term used herein according to the meaning of that term given to it in the aforesaid '031 patent). Efficient lifting was also achieved in the embodiments of the invention disclosed in the '031 patent, while at the same time, the ability to carry more load in a lesser confined space than the known leaf spring lift design resulted. For the first known time then, the '031 patent disclosed a truly effective parallelogram type lift axle suspension system.
While advantageous, as well as being safe and effective for their intended purpose, the specific embodiments set forth in this '031 patent (as commercially exemplified, as aforesaid, by the Hendrickson Paralift™ and Paralift Ultra™ steerable and non-steerable lift axle suspension systems) were in need of further inventive improvement in order to meet certain particularly specialized applications in the vehicle art. For example, as illustrated in the figures of this '031 patent and with particular reference to the location of the lift bellows as shown in FIG. 4 thereof, reproduced here as. FIG. 1 (PRIOR ART), frame hanger bracket 61 is pivotally attached to the first ends of upper control arm 65 and lower control arm 67. From each of these control arms there then extends in the inboard direction, as shown by the arrow labeled accordingly, a pair of opposing appendages 77A, 77B between which the lift air bellows 79 is operatively located. When operated, the air bellows 79 expands and contracts in a “bi-directional” manner, advantageous to the life expectancy of the bellows.
As in the case of the '031 patent, so here, the term “bi-directional” expansion and contraction may be defined in two synonymous ways. The first definition is in terms of the direction of expansion. The second definition is in terms of the angular relationship of the opposing end plates at opposite ends of the lift bellows during expansion and/or contraction. Pursuant to the first definition, the term “bi-directional,” may be said to mean that the lift bellows expands (and/or contracts) in two linearly substantially opposite directions, thus, dividing the lifting (and lowering) forces of the bellows (but not necessarily equally) between the upper and lower control arms. A second and synonymous manner of defining the term “bi-directional,” as is demonstrated by the operation of the '031 patent suspension as well as the suspensions of the preferred embodiments of this invention as described below, is with reference to the angular relationship between the two end plates of the lift bellows “bi-directional” is here defined in this second definition as the angular relationship between the two opposing end plates remaining substantially the same throughout expansion and contraction.
With reference, in this respect, to FIG. 1 (PRIOR ART) and the drawings of the '031 patent, this latter definition of “bi-directional” refers to the angular relationship between end plates 81 (FIG. 1) and 83. (End plates 83 are not shown in FIG. 1, but are shown in other drawings of the '031 patent). A principal purpose of this bi-directional feature is to avoid the detrimental life-shortening effect on the lift bellows as well as efficiency problems caused by the “accordion effect” as more fully described and illustrated in the '031 patent.
While the most preferred way of overcoming this “accordion effect” is to insure no change at all in the angular relationship between a lift bellows' two opposing end plates, some angular change is at times acceptable. Generally speaking, however, to be “bi-directional” as used herein, the angular relationship should not vary by more than about 8°, preferably less than about 3° and most preferably less than about 1° (i.e., 1° being essentially zero except for minor changes caused, for example, by the resiliency of the bushings in the pivot connections at the ends of the control arms). Moreover, and in this respect, it is to be understood that “bi-directional” expansion and contraction does not require that the relationship between the two opposing end plates of a lift bellows be parallel (although this is the preferred embodiment). Instead of parallel, the end plates may be offset at an angle from each other up to a few degrees from parallel (e.g., 2-10°), the important feature being that to be “bi-directional,” whatever the angular relationship is, offset or parallel, this angular relationship should remain substantially the same throughout expansion and contract of the lift bellows during operation of the suspension. By achieving this “bi-directional” mode of expansion/contraction a better efficiency of the lift operation and reduced wear on the rubber portion of the bellows is achieved.
The lift suspensions embodying the '031 patent have as aforesaid proven to be highly commercially successful and safe for their intended purpose. However, in practice, and with reference again to FIG. 1 (PRIOR ART), it has now been found that the embodiments described and illustrated in the '031 patent [as represented here by FIG. 1 (PRIOR ART)] are not truly usable on certain vehicles which otherwise could advantageously employ such a lift suspension. This is particularly true for certain vehicles when the auxiliary lift axle suspension is to be placed in the so-called “pusher” position, i.e., forward of the rear drive axle (and, of course, rearward of the front axle). This is because in certain vehicles there exists various componentry which limits the space between the longitudinal frames of the vehicle that would otherwise be used to accommodate portions of the lift suspension. As will be noted from FIG. 1 (PRIOR ART) in the embodiments disclosed in the '031 patent, lift bellows 79 is offset a substantial distance in the inboard direction from the center line CL of upper control arm 65 and lower control arm 67. Stated another way, the longitudinal control axis AL of lift bellows 79 is inset in the inboard direction (see arrow) a significant distance from under the outside longitudinal frame member 63 of the vehicle so as to be outside the two planes P1 and P2 defined by opposing preferable edges of control arms 65 and 76. If, then, there exists componentry such as a drive shaft, PTO, hydraulic pump, etc., at this location where bellows 79 must reside, the highly advantageous bi-directional, parallelogram lift suspensions of the '031 patent heretofore could not be used.
In view of the above and despite the highly advantageous nature of the invention in the '031 patent, there, thus, arose a need in the art for a new lift axle suspension system which captures the benefits of the suspension of the '031 patent, but which avoids the limiting configuration problem as described above.
It is a purpose of this invention to fulfill this and other needs in the art which will become more apparent to the skilled artisan once given the following disclosure.